Maintaining a data structure with data set names and pointers to a plurality of catalogs

ABSTRACT

A plurality of catalogs are maintained, and wherein each catalog of the plurality of catalogs includes data sets and attributes of the data sets. An indication that a new data set is to be defined is received. A selected catalog is determined from the plurality of catalogs, wherein the selected catalog is suitable for including the new data set and attributes of the new data set. An entry that indicates a data set name corresponding to the new data set and an index to the selected catalog is inserted in a group table.

BACKGROUND

1. Field

The disclosure relates to a method, a system, and an article ofmanufacture for maintaining a data structure with data set names andpointers to a plurality of catalogs.

2. Background

A data set is a logical representation of data that is stored in acomputational system. For example, a file is data set that is maintainedin certain operating systems. Certain operating system maintain aplurality of user catalogs, wherein each user catalog stores directly orindirectly a plurality of data sets and also stores attributes of theplurality of data sets.

A master catalog may be maintained in certain operating systems, whereina catalog alias may provide a means for directing search requests fordata sets to a single user catalog based on the high level qualifiercorresponding to a data set entry.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, a system, an article of manufacture, and a methodfor deploying computing infrastructure, wherein a plurality of catalogsare maintained, and wherein each catalog of the plurality of catalogsincludes data sets and attributes of the data sets. An indication that anew data set is to be defined is received. A selected catalog isdetermined from the plurality of catalogs, wherein the selected catalogis suitable for including the new data set and attributes of the newdata set. An entry that indicates a data set name corresponding to thenew data set and an index to the selected catalog is inserted in a grouptable.

In additional embodiments, a determination is made that a selected dataset is to be deleted. A selected entry corresponding to the selecteddata set is deleted in the group table.

In yet additional embodiments, a determination is made that an attributeof a selected data set is to be modified. A selected catalog of theplurality of catalogs is updated with modifications to the attribute,wherein the selected catalog includes the selected data set, and whereinany change to the group table is avoided.

In further embodiments, a determination is made that an error occurswhile performing at least one of an update to a data set and a readaccess on the data set. A further determination is made as to whichcatalog causes the error. A suitable catalog to which the data setshould be moved is determined. One or more entries of the group tableare updated, in response to moving the data set to the determinedsuitable catalog.

In still further embodiments, determining a selected catalog from theplurality of catalogs is based on: an amount of available space on eachof the plurality of catalogs, wherein those catalogs that have greateravailable space are preferred as the selected catalog over thosecatalogs that have lesser available space; and an amount of contentionactivity on each of the plurality of catalogs, wherein those catalogsthat have lesser contention activity are preferred as the selectedcatalog over those catalogs that have greater contention activity,wherein access by a plurality of threads or processes of one catalogcauses contention among the plurality or threads or processes thataccess the one catalog.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a first computational deviceincluded in a first computing environment, in accordance with certainembodiments;

FIG. 2 illustrates a block diagram of a second computational deviceincluded in a second computing environment, in accordance with certainembodiments;

FIG. 3 illustrates a flowchart that shows operations performed inresponse to definition of new data sets, deletion of data sets, andchanges in attributes of data sets, in accordance with certainembodiments;

FIG. 4 illustrates a block diagram of a mapper data structure, inaccordance with certain embodiments;

FIG. 5 illustrates a flowchart that shows operations for reorganizingentries of a group table in response to errors associated with acatalog, in accordance with certain embodiments;

FIG. 6 illustrates a flowchart that shows operations for insertion ofentries in a group table, in accordance with certain embodiments;

FIG. 7 illustrates a flowchart that shows operations for deletion ofentries in a group table and for updating attributes of a data set inaccordance with certain embodiments;

FIG. 8 illustrates a flowchart that shows operations performed inresponse to an error in a catalog, in accordance with certainembodiments; and

FIG. 9 illustrates a block diagram that shows certain elements that maybe included in the computational device of FIG. 2, in accordance withcertain embodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made.

Master Catalog, User Catalogs, and Group Table

FIG. 1 illustrates a block diagram of a first computing environment 100that includes a first computational device 102, in accordance withcertain embodiments. The computational device 100 may include anoperating system 104, applications 106 that may execute in a pluralityof threads, and data sets 108. A single master catalog 110 that includesa catalog alias 112 that directs (reference numeral 114) requests fordata sets to user catalogs 116 a . . . 116 p is also included in thefirst computational device 102, wherein the user catalogs 116 a . . .116 p are also referred to as catalogs.

The master catalog 110 is one of the users of shared resources and themaser catalog 110 maintains the plurality of catalogs 116 a . . . 116 p.A catalog, such as any of the catalogs 116 a . . . 116 n, alsorepresents one of the main bottlenecks affecting the applications 106since the applications 106 are reliant on the catalog to locate datasets that are needed. When an application executes in multiple threads,parallel requests to a single catalog where all of the application'sdata resides may lead to contention. The ability to reduce some of thiscontention may benefit overall performance.

Certain embodiments provide a mechanism in which a catalog alias pointsto a set of catalogs rather than to a single catalog. Aliases provide ameans to direct search requests to a single user catalog based on a highlevel qualifier of a data set entry. Allowing the Alias to resolve to agroup of catalogs may relieve contention as requests to update/readentries under this alias may be spread out among a plurality ofcatalogs. In addition to contention relief, certain embodiments alsoallow for a recovery from catalog error. If one of the catalogs in acatalog group ceases to function properly, entries from this catalog aremoved to other catalogs in the group.

In certain embodiments, a group table is maintained in cache for eachcatalog group. The group table stores each data set name appended withan index corresponding to the catalog in the group that contains theactual data set entry. In certain embodiments, incoming define activityof new entries may proceed to the catalog within the group with the mostavailable space and least contention activity and a corresponding entrymay be inserted in the group table. Contention is not significant in thegroup table, since the group table is only updated when a new dataset isdefined or when an existing data set is deleted. The group table is notupdated when attributes (e.g., extent information) of a data set change.The information related to the attributes is kept in the user catalogs.Therefore, the majority of operations on the group table may be readactivity which may be suitable for a cache that stores the group table.

Recovery from catalog error may be invoked by monitoring internalcatalog errors. If update/read access operations encounter an error,certain embodiments invoke a sequential read of the problem catalog inan attempt to salvage all possible entries that correspond to theproblem catalog. As each entry is encountered, an operation may beinvoked for selecting the best catalog in the group to substitute theproblem catalog in the entries that point to the problem catalog.

Certain embodiments assign data sets to existing or new user catalogsregardless of the name of the new user catalogs. The name, alias, anduser catalog are not tied together. This additional flexibility allows abetter balancing of data sets across large pools of user catalogs, asexisting catalogs fill up or exhibit performance degradation.

Exemplary Embodiments

FIG. 2 illustrates a block diagram of a second computing environment 200that includes a second computational device 202, in accordance withcertain embodiments. The computational device 202 may include anoperating system 204, applications 206 that may execute in a pluralityof threads, data sets 208, and a catalog management application 210. Thecomputational device also includes a single master catalog 212 thatincludes a catalog alias 214 to direct requests for data sets to a grouptable 216 that includes entries with data sets names 218 a . . . 218 rand associated indexes 220 a . . . 220 r, wherein the indexes 220 a . .. 220 r point to user catalogs 222 a . . . 222 n.

The computational device 202 may comprise any suitable computationaldevice known in the art, including a mainframe computer, a minicomputer, a personal computer, a server, a client, a host, a telephonydevice, a storage controller, etc. The catalog management application210 is an application that may be implemented in hardware, firmware,software or any combination thereof. In certain embodiments, the catalogmanagement application 210 may be included as part of the operatingsystem 204.

The group table 216 is a data structure that may be implemented in acache of the computation device 202. The group table 216 may beimplemented as a table, a list, a set of pointers or references, or asany other suitable data structure. Corresponding to each data set namethere is an index in the group table 216. For example, data set name 218a has a corresponding index 220 a, and data set name 218 r has acorresponding index 220 r. Each index points to a user catalog of theplurality of user catalogs. For example, index 220 a may point to usercatalog 222 a if the user catalog 222 a includes the data set and theattributes corresponding to the data set name 218 a. The group table 216is relatively small is size in comparison to the catalogs 222 a . . .222 n and can be readily updated or accessed. In alternative embodimentsthere may be a plurality of group tables.

FIG. 3 illustrates a flowchart that shows operations performed inresponse to definition of new data sets, deletion of data sets, andchanges in attributes of data sets, in accordance with certainembodiments. The operations shown in FIG. 3 may be performed by thecatalog management application 210 implemented in the computationaldevice 202 of the computing environment 200.

Control starts (at block 300) and the catalog management application 210makes a determination (at block 302) as to whether an operation is adata set related operation. If so, control may proceed in parallel toblocks 304, 306, 308. If not, control returns to block 300.

At block 304, the catalog management application 210 determines whethera new data set is to be defined. If so, then the catalog managementapplication 210 determines (at block 310) a user catalog from theplurality of user catalogs 222 a . . . 222 n based on the followingfactors:

-   (1) amount of available space in each of the user catalogs 222 a . .    . 222 n, wherein the more space a user catalog has the better is the    user catalog for storing the new data set and the attributes of the    new data set; and-   (2) the amount of contention activity in each of the user catalogs    222 a . . . 222 n, wherein the less contention activity a user    catalog has the better is the user catalog for storing the new data    set and the attributes of the new data set.

From block 310, control proceeds to block 312 in which the catalogmanagement application 210 defines, i.e., inserts, a new entry in thegroup table 216 corresponding to the new data set name and an associatedindex that points to the determined user catalog in block 310. Fromblock 312 control proceeds to block 314 where the process stops. If nonew data set is to be defined at block 304 then control also proceeds toblock 314 where the process stops.

At block 306, the catalog management application 210 determines whetheran existing data set is to be deleted. If so, the catalog managementapplication 210 deletes (at block 316) in the group table 216 the dataset name and the associated index corresponding to the existing dataset, and control proceeds to block 314 where the process stops. If atblock 306, the catalog management application 210 determines that anexisting data set is not be deleted control proceeds to block 314 wherethe process stops.

At block 308, the catalog management application 210 determines if thereis a change in attributes of a data set. If so, no changes have to bemade to the group table 216 but the user catalog selected from the usercatalogs 222 a . . . 222 n that stores the attributes of the data set ismodified (at block 318) to change the attributes, and the process stops(at block 314). If at block 308, the catalog management application 210determines if there is no change in attributes of a data set thencontrol proceeds to block 314 where the process stops.

Therefore, FIG. 3 illustrates certain embodiments in which the grouptable 216 is modified in response to definitions of new data sets anddeletions of existing data sets.

FIG. 4 illustrates a block diagram of a mapper data structure 400, inaccordance with certain embodiments. The mapper data structure 400includes a plurality of qualifiers 402 a, 402 b . . . 402 s, wherein 402a is the highest level qualifier and 402 s is the lowest levelqualifier. Each qualifier may be a sequence of bits or bytes. However,the qualifiers may also be represented via other mechanisms. One or morequalifiers that correspond to an exemplary data set 404 are mapped todetermine the user catalog corresponding to the data set 404. Forexample, in certain embodiments, the resolution of qualifiers (shown byreference numeral 406) is based on resolution of the highest levelqualifier 402 a to determine (reference numeral 408) the user catalogcorresponding to the data set 404.

FIG. 5 illustrates a flowchart that shows operations for reorganizingentries of a group table in response to errors associated with acatalog, in accordance with certain embodiments. The operations shown inFIG. 5 may be performed by the catalog management application 210implemented in the computational device 202 of the computing environment200.

Control starts (at block 500) and proceeds to block 502 in which thecatalog management application 210 determines whether an error occurswhile performing updates to a data set or while performing read accesson a data set. If so, the catalog management application determines (atblock 504) the user catalog (e.g., one of the user catalogs 222 a . . .222 n) that is causing the error and then invokes (at block 506) asequential read on the determined catalog that is causing the error. Foreach entry of the determined user catalog that is causing the error, thecatalog management application 210 determines (at block 508) a suitablecatalog (according to some optimality criteria) to which the data setshould be moved and then updates the group table 216 accordingly, andsubsequently the process stops (at block 510). The process also stops(at block 510) if the catalog management application 210 determines (atblock 502) that no error occurs while performing updates to a data setor while performing read access on a data set.

FIG. 6 illustrates a flowchart that shows operations for insertion ofentries in a group table, in accordance with certain embodiments. Theoperations shown in FIG. 6 may be performed by the catalog managementapplication 210 implemented in the computational device 202 of thecomputing environment 200.

Control starts at block 600 in which the catalog management application210 maintains a plurality of catalogs 222 a . . . 222 n, and whereineach catalog of the plurality of catalogs 222 a . . . 222 n includesdata sets and attributes of the data sets. The catalog managementapplication 210 receives (at block 602) an indication that a new dataset is to be defined.

Control proceeds to block 604, where that catalog management application210 determines a selected catalog from the plurality of catalogs 222 a .. . 222 n, wherein the selected catalog is suitable for including thenew data set and attributes of the new data set. The determining of theselected catalog from the plurality of catalogs is based on:

-   (i) an amount of available space on each of the plurality of    catalogs 222 a . . . 222 n, wherein those catalogs that have greater    available space are preferred as the selected catalog over those    catalogs that have lesser available space; and-   (ii) an amount of contention activity on each of the plurality of    catalogs 222 a . . . 222 n, wherein those catalogs that have lesser    contention activity are preferred as the selected catalog over those    catalogs that have greater contention activity, wherein access by a    plurality of threads or processes of one catalog causes contention    among the plurality or threads or processes that access the one    catalog.

From block 604 control proceeds to block 606 where the catalogmanagement application inserts an entry that indicates a data set namecorresponding to the new data set and an index in the group table 216.

Therefore, FIG. 6 illustrates certain embodiments in which a new dataset is defined by inserting an entry having a data set name and an indexinto the group table 216.

FIG. 7 illustrates a flowchart that shows operations for deletion ofentries in a group table and for updating attributes of a data set inaccordance with certain embodiments. The operations shown in FIG. 7 maybe performed by the catalog management application 210 implemented inthe computational device 202 of the computing environment 200.

Control starts at block 700 and proceeds in parallel to blocks 702 and704. At block 702 the catalog management application 210 determines thatthat a selected data set is to be deleted. The catalog managementapplication 210 deletes (at block 706) a selected entry corresponding tothe selected data in the group table 216, and the process stops (atblock 708).

At block 704, the catalog management application 210 determines that anattribute of a selected data set is to be modified. The catalogmanagement application 210 updates (at block 710) a selected catalog ofthe plurality of catalogs 222 a . . . 222 n with modifications to theattribute, wherein the selected catalog includes the selected data set,and wherein any change to the group table 216 is avoided.

Therefore, FIG. 7 illustrates certain embodiments in which data sets aredeleted by updating the group table 216 and attributes of data sets areupdated by updating the appropriate user catalog 222 a . . . 222 n.

FIG. 8 illustrates a flowchart that shows operations performed inresponse to an error in a catalog, in accordance with certainembodiments. The operations shown in FIG. 8 may be performed by thecatalog management application 210 implemented in the computationaldevice 202 of the computing environment 200.

Control starts at block 800 where the catalog management application 210determines that an error has occurred while performing at least one ofan update to a data set and a read access on the data set. The catalogmanagement application 210 determines (at block 802) which catalog hascaused the error. Then the catalog management application 210 determines(at block 804) a suitable catalog to which the data set should be moved.The catalog management application 210 updates (at block 806) one ormore entries of the group table 216, in response to moving the data setto the determined suitable catalog.

Therefore, FIG. 8 illustrates certain embodiments in which the catalogmanagement application 210 updates the group table 216 in response to anerror generated in a catalog that includes a data set.

Certain embodiments described in FIGS. 1-8 maintain a group table 216 incache, wherein the group table 216 is used to direct requests to anappropriate user catalog for a data set. Updates the group table 216 arerelatively less time consuming in comparison to updates to the usercatalogs. Additionally, the size of the group table 216 is smaller incomparison to the user catalogs because the group table stores only dataset names and corresponding indexes to the user catalogs. Furthermore,in response to a catalog error, alternative catalogs may be used and thegroup table 216 may be updated accordingly.

In certain alternative embodiments, there may be one or more additionalgroup tables beyond the exemplary group table 216 shown in FIG. 2, i.e.,there may be a plurality of group tables implemented in thecomputational device 202. In such embodiments, the alias structure maydirect the data set entry to a specific group table of the plurality ofgroup tables. For example, the alias structure may direct a data setentry to the exemplary group table 216. The exemplary group table 216may then direct the data set entry into a specific user catalog selectedfrom the user catalogs 222 a . . . 222 n.

Additional Embodiment Details

The described techniques may be implemented as a method, apparatus orarticle of manufacture involving software, firmware, micro-code,hardware and/or any combination thereof. The term “article ofmanufacture” as used herein refers to code or logic implemented in amedium, where such medium may comprise hardware logic [e.g., anintegrated circuit chip, Programmable Gate Array (PGA), ApplicationSpecific Integrated Circuit (ASIC), etc.] or a computer readable storagemedium, such as magnetic storage medium (e.g., hard disk drives, floppydisks, tape, etc.), optical storage (CD-ROMs, optical disks, etc.),volatile and non-volatile memory devices [e.g., Electrically ErasableProgrammable Read Only Memory (EEPROM), Read Only Memory (ROM),Programmable Read Only Memory (PROM), Random Access Memory (RAM),Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM),flash, firmware, programmable logic, etc.]. Code in the computerreadable storage medium is accessed and executed by a processor. Themedium in which the code or logic is encoded may also comprisetransmission signals propagating through space or a transmission media,such as an optical fiber, copper wire, etc. The transmission signal inwhich the code or logic is encoded may further comprise a wirelesssignal, satellite transmission, radio waves, infrared signals,Bluetooth, etc. The transmission signal in which the code or logic isencoded is capable of being transmitted by a transmitting station andreceived by a receiving station, where the code or logic encoded in thetransmission signal may be decoded and stored in hardware or a computerreadable medium at the receiving and transmitting stations or devices.Additionally, the “article of manufacture” may comprise a combination ofhardware and software components in which the code is embodied,processed, and executed. Of course, those skilled in the art willrecognize that many modifications may be made without departing from thescope of embodiments, and that the article of manufacture may compriseany information bearing medium. For example, the article of manufacturecomprises a storage medium having stored therein instructions that whenexecuted by a machine results in operations being performed.

Certain embodiments can take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment containingboth hardware and software elements. In a preferred embodiment, theinvention is implemented in software, which includes but is not limitedto firmware, resident software, microcode, etc.

Furthermore, certain embodiments can take the form of a computer programproduct accessible from a computer usable or computer readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer usable or computer readable medium can be any apparatus thatcan contain, store, communicate, propagate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device. The medium can be an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system (orapparatus or device) or a propagation medium. Examples of acomputer-readable medium include a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk and an opticaldisk. Current examples of optical disks include compact disk-read onlymemory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

The terms “certain embodiments”, “an embodiment”, “embodiment”,“embodiments”, “the embodiment”, “the embodiments”, “one or moreembodiments”, “some embodiments”, and “one embodiment” mean one or more(but not all) embodiments unless expressly specified otherwise. Theterms “including”, “comprising”, “having” and variations thereof mean“including but not limited to”, unless expressly specified otherwise.The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise. Theterms “a”, “an” and “the” mean “one or more”, unless expressly specifiedotherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries. Additionally, a description of an embodiment withseveral components in communication with each other does not imply thatall such components are required. On the contrary a variety of optionalcomponents are described to illustrate the wide variety of possibleembodiments.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously, inparallel, or concurrently.

When a single device or article is described herein, it will be apparentthat more than one device/article (whether or not they cooperate) may beused in place of a single device/article. Similarly, where more than onedevice or article is described herein (whether or not they cooperate),it will be apparent that a single device/article may be used in place ofthe more than one device or article. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments need not include thedevice itself.

FIG. 9 illustrates a block diagram that shows certain elements that maybe included in the computational device 202 of FIG. 2, in accordancewith certain embodiments. One or more of the computational devices 202either individually or collectively may also be referred to as a system900, and may include a circuitry 902 that may in certain embodimentsinclude a processor 904. The system 900 may also include a memory 906(e.g., a volatile memory device), and storage 908. The storage 908 mayinclude a non-volatile memory device (e.g., EEPROM, ROM, PROM, RAM,DRAM, SRAM, flash, firmware, programmable logic, etc.), magnetic diskdrive, optical disk drive, tape drive, etc. The storage 908 may comprisean internal storage device, an attached storage device and/or a networkaccessible storage device. The system 900 may include a program logic910 including code 912 that may be loaded into the memory 906 andexecuted by the processor 904 or circuitry 902. In certain embodiments,the program logic 910 including code 912 may be stored in the storage908. In certain other embodiments, the program logic 910 may beimplemented in the circuitry 902. Therefore, while FIG. 9 shows theprogram logic 910 separately from the other elements, the program logic910 may be implemented in the memory 906 and/or the circuitry 902.

Certain embodiments may be directed to a method for deploying computinginstruction by a person or automated processing integratingcomputer-readable code into a computing system, wherein the code incombination with the computing system is enabled to perform theoperations of the described embodiments.

At least certain of the operations illustrated in FIGS. 1-9 may beperformed in parallel as well as sequentially. In alternativeembodiments, certain of the operations may be performed in a differentorder, modified or removed.

Furthermore, many of the software and hardware components have beendescribed in separate modules for purposes of illustration. Suchcomponents may be integrated into a fewer number of components ordivided into a larger number of components. Additionally, certainoperations described as performed by a specific component may beperformed by other components.

The data structures and components shown or referred to in FIGS. 1-9 aredescribed as having specific types of information. In alternativeembodiments, the data structures and components may be structureddifferently and have fewer, more or different fields or differentfunctions than those shown or referred to in the figures. Therefore, theforegoing description of the embodiments has been presented for thepurposes of illustration and description. It is not intended to beexhaustive or to limit the embodiments to the precise form disclosed.Many modifications and variations are possible in light of the aboveteaching.

1. A method, comprising: maintaining, via a processor, a single mastercatalog having a catalog alias and a plurality of user catalogs, whereineach user catalog of the plurality of user catalogs includes data setsand attributes of the data sets; storing, in a group table that issmaller in size than the plurality of user catalogs, data set names andcorresponding indexes to the plurality of user catalogs, and pointingvia the group table, the catalog alias of the single master catalog tothe plurality of user catalogs, wherein the group table is stored in acache; receiving, via the processor, an indication that a new data setis to be defined; determining, via the processor, a selected usercatalog from the plurality of user catalogs, based on an amount ofavailable space on each of the plurality of user catalogs and an amountof contention activity on each of the plurality of user catalogs,wherein the selected user catalog is suitable for including the new dataset and attributes of the new data set; subsequent to determining theselected user catalog, inserting via the processor, in the group table,an entry that indicates a data set name corresponding to the new dataset and an index to the selected catalog; and directing, by the catalogalias of the single master catalog, requests for any data sets to thegroup table, wherein: in response to determining that an attribute of aselected data set is to be modified, a selected user catalog of theplurality of user catalogs is updated with modifications to theattribute, wherein the selected user catalog includes the selected dataset, and wherein any change to the group table is avoided while theplurality of user catalogs is updated; and the group table is updatedonly when one or more new datasets are defined or when one or moreexisting datasets are modified, wherein updating of the group table isperformed in a relatively lesser amount of time in comparison to updatesto the plurality of user catalogs.
 2. The method of claim 1, the methodfurther comprising: determining that a selected data set is to bedeleted; deleting, in the group table, via the directing by the catalogalias of the single master catalog, a selected entry corresponding tothe selected data set.
 3. The method of claim 1, the method furthercomprising: determining that an error occurs while performing at leastone of an update to a data set and a read access on the data set; anddetermining which user catalog causes the error; determine a suitableuser catalog to which the data set should be moved; update one or moreentries of the group table, in response to moving the data set to thedetermined suitable user catalog.
 4. The method of claim 1, the methodfurther comprising: preferring as the selected user catalog those usercatalogs that have greater available space over those user catalogs thathave lesser available space; and preferring as the selected user catalogthose user catalogs that have lesser contention activity over those usercatalogs that have greater contention activity, wherein access by aplurality of threads or processes of one user catalog causes contentionamong the plurality or threads or processes that access the one usercatalog.
 5. A system, comprising: a memory; and a processor coupled tothe memory, wherein the processor executes operations, the operationscomprising: maintaining a single master catalog having a catalog aliasand a plurality of user catalogs, wherein each user catalog of theplurality of user catalogs includes data sets and attributes of the datasets; storing, in a group table that is smaller in size than theplurality of user catalogs, data set names and corresponding indexes tothe plurality of user catalogs, and pointing via the group table, thecatalog alias of the single master catalog to the plurality of usercatalogs, wherein the group table is stored in a cache; receiving anindication that a new data set is to be defined; determining a selecteduser catalog from the plurality of user catalogs, based on an amount ofavailable space on each of the plurality of user catalogs and an amountof contention activity on each of the plurality of user catalogs,wherein the selected user catalog is suitable for including the new dataset and attributes of the new data set; subsequent to determining theselected user catalog, inserting via the processor, in the group table,an entry that indicates a data set name corresponding to the new dataset and an index to the selected catalog; and directing, by the catalogalias of the single master catalog, requests for any data sets to thegroup table, wherein: in response to determining that an attribute of aselected data set is to be modified, a selected user catalog of theplurality of user catalogs is updated with modifications to theattribute, wherein the selected user catalog includes the selected dataset, and wherein any change to the group table is avoided while theplurality of user catalogs is updated; and the group table is updatedonly when one or more new datasets are defined or when one or moreexisting datasets are modified, wherein updating of the group table isperformed in a relatively lesser amount of time in comparison to updatesto the plurality of user catalogs.
 6. The system of claim 5, theoperations further comprising: determining that a selected data set isto be deleted; deleting, in the group table, via the directing by thecatalog alias of the single master catalog, a selected entrycorresponding to the selected data set.
 7. The system of claim 5, theoperations further comprising: determining that an error occurs whileperforming at least one of an update to a data set and a read access onthe data set; and determining which user catalog causes the error;determine a suitable user catalog to which the data set should be moved;update one or more entries of the group table, in response to moving thedata set to the determined suitable user catalog.
 8. The system of claim5, the operations further comprising: preferring as the selected usercatalog those user catalogs that have greater available space over thoseuser catalogs that have lesser available space; and preferring as theselected user catalog those user catalogs that have lesser contentionactivity over those user catalogs that have greater contention activity,wherein access by a plurality of threads or processes of one usercatalog causes contention among the plurality or threads or processesthat access the one user catalog.
 9. A computer readable storage medium,wherein code stored in the computer readable storage medium whenexecuted by a processor causes operations, the operations comprising:maintaining a single master catalog having a catalog alias and aplurality of user catalogs, wherein each user catalog of the pluralityof user catalogs includes data sets and attributes of the data sets;storing, in a group table that is smaller in size than the plurality ofuser catalogs, data set names and corresponding indexes to the pluralityof user catalogs, and pointing via the group table, the catalog alias ofthe single master catalog to the plurality of user catalogs, wherein thegroup table is stored in a cache; receiving an indication that a newdata set is to be defined; determining a selected user catalog from theplurality of user catalogs, based on an amount of available space oneach of the plurality of user catalogs and an amount of contentionactivity on each of the plurality of user catalogs, wherein the selecteduser catalog is suitable for including the new data set and attributesof the new data set; subsequent to determining the selected usercatalog, inserting via the processor, in the group table, an entry thatindicates a data set name corresponding to the new data set and an indexto the selected catalog; and directing, by the catalog alias of thesingle master catalog, requests for any data sets to the group table,wherein: in response to determining that an attribute of a selected dataset is to be modified, a selected user catalog of the plurality of usercatalogs is updated with modifications to the attribute, wherein theselected user catalog includes the selected data set, and wherein anychange to the group table is avoided while the plurality of usercatalogs is updated; and the group table is updated only when one ormore new datasets are defined or when one or more existing datasets aremodified, wherein updating of the group table is performed in arelatively lesser amount of time in comparison to updates to theplurality of user catalogs.
 10. The computer readable storage medium ofclaim 9, the operations further comprising: determining that a selecteddata set is to be deleted; deleting, in the group table, via thedirecting by the catalog alias of the single master catalog, a selectedentry corresponding to the selected data set.
 11. The computer readablestorage medium of claim 9, the operations further comprising:determining that an error occurs while performing at least one of anupdate to a data set and a read access on the data set; and determiningwhich user catalog causes the error; determine a suitable user catalogto which the data set should be moved; update one or more entries of thegroup table, in response to moving the data set to the determinedsuitable user catalog.
 12. The computer readable storage medium of claim9, the operations further comprising: preferring as the selected usercatalog those user catalogs that have greater available space over thoseuser catalogs that have lesser available space; and preferring as theselected user catalog those user catalogs that have lesser contentionactivity over those user catalogs that have greater contention activity,wherein access by a plurality of threads or processes of one usercatalog causes contention among the plurality or threads or processesthat access the one user catalog.